The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component or line than can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.
In the manufacture of integrated circuits (IC), or chips, patterns representing different layers of the chip are created on a series of reusable photomasks (also referred to herein as masks) in order to transfer the design of each chip layer onto a semiconductor substrate during the manufacturing process. These layers are built up using a sequence of processes and translate into the tiny transistors and electrical circuits that comprise each completed chip. Thus, any defects in the mask may be transferred to the chip, potentially adversely effecting performance. Defects that are severe enough may render the mask completely useless. A reflective mask is used during extreme ultra-violet (EUV) lithography. To provide a higher resolution benefited by the EUV lithography, a high quality of the reflective mask with low defects is eagerly needed.